affinity

Examples of affinity in the following topics:

• Primary Active Transport

  • With the enzyme oriented towards the interior of the cell, the carrier has a high affinity for sodium ions.
  • The protein's affinity for sodium decreases, and the three sodium ions leave the carrier.
  • The shape change increases the carrier's affinity for potassium ions, and two such ions attach to the protein.
  • The carrier protein, in its new configuration, has a decreased affinity for potassium, and the two ions are released into the cytoplasm.
  • The protein now has a higher affinity for sodium ions, and the process starts again.

• Antibody Functions

  • In fact, antibodies exhibit different affinities (attraction) depending on the molecular complementarity between antigen and antibody molecules .
  • An antibody with a higher affinity for a particular antigen would bind more strongly and stably.
  • Although avidity measures the strength of binding, just as affinity does, the avidity is not simply the sum of the affinities of the antibodies in a multimeric structure.
  • Typically, multimeric antibodies, such as pentameric IgM, are classified as having lower affinity than monomeric antibodies, but high avidity.

• Transport of Oxygen in the Blood

  • The increase in carbon dioxide and subsequent decrease in pH reduce the affinity of hemoglobin for oxygen.
  • Increased temperature, such as from increased activity of skeletal muscle, causes the affinity of hemoglobin for oxygen to be reduced.
  • However, the affinity of hemoglobin for oxygen may shift to the left or the right depending on environmental conditions.

• Control of Metabolism Through Enzyme Regulation

  • Their binding induces a conformational change that reduces the affinity of the enzyme's active site for its substrate. 
  • They bind to an allosteric site which induces a conformational change that increases the affinity of the enzyme's active site for its substrate.
  • In contrast, allosteric activators modify the active site of the enzyme so that the affinity for the substrate increases.

• Regulatory Mechanisms for Cellular Respiration

  • This alteration of the protein's (the enzyme's) structure either increases or decreases its affinity for its substrate, with the effect of increasing or decreasing the rate of the reaction.

• Catabolite Activator Protein (CAP): An Activator Regulator

  • Two cAMP molecules bind dimeric CAP with negative cooperativity and function as allosteric effectors by increasing the protein's affinity for DNA.

• Transport of Carbon Dioxide in the Blood

  • Carbon monoxide has a greater affinity for hemoglobin than does oxygen.

• Endocytosis

  • A targeted variation of endocytosis, known as receptor-mediated endocytosis, employs receptor proteins in the plasma membrane that have a specific binding affinity for certain substances .

• ATP in Metabolism

  • Phosphorylation by ATP alters the structure of the integral protein that functions as the pump, changing its affinity for sodium and potassium.